The form that MO uses doesn't differentiate. It asks for gross monthly income... if the bonus is consistent (and 6 months is considered consistent), then it should be included. If it's NOT, you can request that the court impute an income based on W-2s for the past 3 years.
Is the bonus significant enough to effect the CS calculation by more than a few dollars? Have you run the numbers on the official MO calculator? I can link you to one you can d/l in excel format if you need it.
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